In certain inbred low leukemia strains of mice, the induction of an immunological disturbance, the graft-versus-host reaction (GVHR) leads to the development of lymphoreticular tumors associated with replication of endogenous murine leukemia virus (MuLV). We are (1) Investigating the causative role of endogenous MuLV in the development of tumors by GVHR mice. (2) Investigating the role of stimulated lymphocytes, both of the B-cell and T-cell series in the replication of the virus. BIBLIOGRAPHIC REFERENCES: Gleichmann, E., Gleichmann, H., Schwartz, R.S., Weinblatt, A., and Armstrong, M.Y. Immunologic Induction of Malignant Lymphoma: Identification of Donor and Host Tumors in the Graft-Versus-Host Model. J. Nat. Cancer Inst. 54: 107, 1975.